clampToHeightMostDetailed fix

[lilleyse]

Fixes #7621

Resolves the promise of clampToHeightMostDetailed and sampleHeightMostDetailed during the postRender event to ensure that entities are never created mid-frame, which is anywhere between viewer._onTick and viewer._postRender.

The order of events in a single render loop is basically:

1. viewer._onTick
2. updateAsyncRayPicks (in scene.render) (this is renamed to updateMostDetailedRayPicks in @loshjawrence's branch)
   2.a. Synchronous pick calls immediately when the async ray is ready
3. viewer._postRender (first subscriber to scene.postRender)
4. The rest of scene.postRender including these new events.

[cesium-concierge]

Thanks for the pull request @lilleyse!

• ✔️ Signed CLA found.
• ❔ Unit tests were not updated.
  • Make sure you've updated tests to reflect your changes, added tests for any new code, and ran the code coverage tool.

Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.
• Works (or fails gracefully) in IE11.

[loshjawrence]

Looks good, works in the staging branch too.

[lilleyse]

Thanks @loshjawrence, I'll merge it in.